Touch-responsive keying circuit for electronic musical instruments

ABSTRACT

In an electronic musical instrument, tone keyer circuits are respectively controlled by touch-responsive keying circuits. The touch-responsive keying circuit comprises: a key switch having a break contact, a make contact and a movable contact; a first charge-discharge circuit having a charging capacitor and a discharging resistor both connected between the movable contact and the ground; an electrical source +B connected to the break contact; a switching transistor with its base connected to the make contact; and a second charge-discharge circuit being provided between the emitter of the transistor and the ground with a second capacitor and with a series circuit of a second resistor and an normally closed switch which is ganged with the key switch, the capacitor being connected to the keyer circuit. While the movable contact of the key switch travels from the break contact to the make contact, the first charge-discharge circuit is discharged with a predetermined time constant. The switching transistor is brought conductive to the extent responsive to a charged voltage remaining in the first chargedischarge circuit at the time the movable contact touches the make contact. The second charge-discharge circuit is charged through the transistor to establish a keying voltage.

United States Patent 1191 Uchiyama Jan.8,1974

[75] Inventor:

[73] Assignee: Nippon Gakki Seizo Kabushiki Kaisha, l-lamamatsu-shi,Shizuoka-ken, Japan 22 Filed: July 20,1972

21 Appl. N01; 273,608

Yasuji Uchiyama, l-Iamakita, Japan [30] Foreign Application PriorityData July 20, 1971 Japan, 46/53580 July 20, 1971 Japan 46/63475 July 20,1971 Japan 46/63476 [52] US. Cl 84/113, 84/126, 84/DIG. 23 [51] Int. Cl.G10h 1/02 [58] Field 01 Search 84/1.01, 1.09, 1.1,

84/113,126, 1.27, DIG. 23; 317/151; 307/108, 265; 320/1 [56] ReferencesCited UNITED STATES PATENTS 3,535,972 10/1970 Teranishi 84/126 3,602,6268/1971 Aramaki 84/1.01

3,626,075 12/1971 Hiyama 84/].13

3,544,699 12/1970 Harris 84/].26

3,626,074 12/1971 Hiyama... 84/1.01

3,627,897 12/1971 Harris 84/l.13 X

, 3,634,594 1/1972 Hiyama 84/l.1

3,636,232 1/1972 Hiyama 84/126 X 3,651,730 3/1972 Adachi ..84/l.26X

, Primary ExaminerRichard B. Wilkinson Assistant ExaminerStanley. JWitkowski AttorneyJohn-C. Holman et al.

[57] I ABSTRACT In an electronic musical instrument, tone keyer circuitsare respectively controlled by touch-responsive keying circuits. Thetouch-responsive keying circuit comprises: a key switch having a breakcontact, a make contact and a movable contact; a first chargedischargecircuit having a charging capacitor and a discharging resistor bothconnected between the movable contact and the ground; an electricalsource +B connected to the break contact; a switchingtransistor with itsbase connected to the make contact; and a second charge-dischargecircuit being provided be tween the emitter of the transistor and theground with a second capacitor and with a series circuit of a secondresistor and an normally closed switch which is ganged with the keyswitch, the capacitor being connected to the keyer circuit. While themovable contact of the key switch travels from the break contact to themake contact, the first charge-discharge circuit is discharged with apredetermined time constant. The switching transistor is broughtconductive to the extent responsive toa charged voltage remaining in thefirst charge-discharge circuit at the time the movable contact touchesthe make contact. The second chargedischarge circuit is charged throughthe transistor to establish a keying voltage.

5 Claims, 7 Drawing Figures Pmmmm emu 3.784.718

SHEET 10F 3 FIG. I

PRIOR ART KEYER CIRCUIT F l G. 2

PRIOR ART f1 f2 f3 TIME- Lh|+---- h2 --4 PAIENIEUJAII 8 i974 SHEEI 2 BF3 TIME fl 12 T3 FIG. 5

TIME

PAIENTEDJAM 8 2914 SREH 3 OF 3 FIG. 6

BACKGROUND OF THE INVENTION The present invention relates generally toelectronic musical instruments and more particularly to atouchresponsive keying circuit to be used in electronic musicalinstruments.

Conventional touch-responsive keying circuits for electronic musicalinstruments have been of a type as shown in FIG. 1 which comprises a keyswitch 1 having stationary contacts b and m and a movable contact 0. Themovable contact c is connected to a first chargedischarge circuit 2consisting of a charging capacitor C and a discharging resistor R andthe break stationary contact b is connected to a D. C. source 3. Themake stationary contact m is connected through a reversecurrent-blockingdiode 4 to a second charge-discharge circuit 5 consisting of a chargingcapacitor C and a discharging resistor R An outputW for keying a keyercircuit 6 is obtained across the second chargedischarge circuit 5.

In this conventional touch-responsive keying circuit 7, as long as a key(not shown) is not depressed, the contact is maintained connected to thecontact b, and therefore the capacitor C is charged through thesecontacts by the D.C. source 3. Under this condition, if the contact 0 isseparated from the contact b at an instant t and is brought into contactwith the contact m at a subsequent instant t by depressing a key, asshown in FIG. 2, the capacitor C, will be discharged through theresistor R during the period of this travelling time (from t to t Inthis connection, the discharge quantity in the case of a shorttravelling period is les than that in the case of a long travellingperiod. Therefore, the voltage of the capacitor C or the output keyingvoltage W in the case of the short travelling period (curve I) isgreater in peak value than that in the case of the long travellingperiod (curves II and Ill). Accordingly, it will be apparent that if thekey-depressing speed is controlled as desired during the playing of anelectronic musical instrument, acoustic volume of the electronic musicalinstrument can be controlled in response to the keydepressing speed.

However, in such a circuit arrangement as described above, when themovable contact c of the switch is moved into contact with the contactm, the electrical current thereby flowing through the contacts 0 and mand the diode 4 is relatively large and, therefore, may damage thecontacts of the switch 1. The damage to the contacts would be serious ifthe travelling time of the contacts of the switch 1 were extremelyshort, as the remaining voltage is high.

Furthermore, it is generally necessary for reasons of performance effectto select the time constants (C,R C R of the charge-discharge circuitsso that the time period b, (FIG. 2) from an instant t when the contact 0of the switch 1 separates from the contact b as a result of akey-depressing operation, to an instant t when the contact c comes intocontact with the contact m during the same operation, is of the order offrom -10 ms to 30 ms, and so that the time period h from the instant twhen the contact c comes into contact with the contact m to an instant twhen the contact c separates from the contact m upon release of the keyis of the order of Therefore, it is necessary to select capacitorshaving considerably large value capacitances for these chargedischargecircuits. In addition, if the time period h, of switching the key switch1 is made extremely long, all of the charge in the capacitor C, will bedischarged through the resistor R as a result of which no output will beproduced.

SUMMARY OF THE INVENTION It is accordingly a primary objectof thepresent invention to provide a touch-responsive keying circuit for anelectronic musical instrument, in which capacitors of small capacitancescan to used in charge-discharge circuits, whereby the contacts having akey switch are protected against damage by an electrical current, theabove-described difficulties accompany the conventional touch-responsivekeying circuit being taken into consideration.

Another object of the present invention is to provide a touch-responsivekeying circuit for an electronic musical instrument, in which its outputcan be obtained even when the travelling time of the key switch is madelonger by a soft keying operation.

A further object of the present invention is to provide atouch-responsive keying circuit for an electronic musical instrumentwhich can ensure the production of a keying output correctly responsiveto a key-depressing speed, with the output level substantially sustainedduring the key depression. 7

A still further object of the present invention is to provide a touchresponsive keying circuit for an electronic musical instrument in whicheither a touchresponsive keying voltage of a level dependent on akey-depressing speed or a touch-irresponsive keying voltage of a levelindependent of the key-depressing speed can be selectively applied tothe tone keyer circuit.

A specific object of the present invention is to provide atouch-responsive keying circuit for an electronic musical instrument inwhich, when a key is depressed very slowly, an output can be obtainedeven if a first charge and discharge circuit has been discharged,whereby a pianissimo performance effect can be easily and stablyrendered as desired.

The foregoing objects and other objects of the present invention willbecome more apparent from the following detailed description and theappended claims when read in conjunction with the accompanying drawings,in which like parts are designated by like reference numerals andcharacters.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is an electrical connection diagram showing a conventionaltouch-responsive keying circuit together with a tone keyer circuit;

FIG. 2 is a chart showing waveforms of the keying voltages for adescription of the operation of the circuit shown in FIG. 1;

FIG. 3 is an electrical connection diagram showing one example of atouch-responsive keying circuit according to the present inventiontogether with a tone keyer circuit;

FIGS. 4 and 5 are waveform charts for a description of the operation ofthe circuit shown in FIG. 3;

FIG. 6 is an equivalent circuit diagramof an essential part of thecircuit shown in FIG. 3; and

FIG. 7 is an electrical connectiondiagram showing another example of thepresent invention together with a tone keyer circuit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Withreference now to FIG. 3, the example of the present invention showntherein comprises a touchresponsive keying circuit 1 1 and a tone keyercircuit 12 whose gating operation is controlled by an output W of thetouch-responsive keying circuit 11. The tone keyer circuit 12 itself isa circuit well known in the art and comprises: a transistor 13 forreceiving the output W of the touch-responsive keyingcircuit 11; atransistor 15 for receiving a musical tone signal I which is applied toa musical tone signal input terminal 14; and a transistor 16 foramplifying a gated output produced by the transistors 13 and 15, wherebyan output musical tone signal whose envelope is defined by the waveformof the addition to the musical tone signal I. The existence of suchother combinations is indicated by the representation 18 in FIG. 3.

The movable contact 0 of a key switch 21 in the touch-responsive keyingcircuit 11 is connected through a resistor R to a first charge-dischargecircuit 22 which comprises a charging capacitor C and a dischargingresistor R and one end of the circuit 22 is connected to ground line E.Furthermore, a break contact b of the key switch 21 is connected to apower source +B (12V), and a make contact m is connected to the base ofa switching transistor 23. The collector of the transistor 23 isconnected to the power source +B. The emitter of the transistor 23 isconnected to a charging capacitor C through a charging resistor R Oneterminal of the capacitor C is grounded, while the other terminalthereof is also grounded through the resistor R.,, a dischargingresistor R and contacts b and c of a switch 27, which is ofa normallyclosed type and gang-operated with the key switch 21. Thus, a secondcharge-discharge circuit 28 is formed with the capacitor C and theresistors R and R The other end of the first charge-discharge circuit 22is connected through a resistor R to the power source +B. The resistor Ris a limiting resistor which serves to limit an electric currentcharging the capacitor C In the circuit described above, as long as anassociated key is not depressed the contacts 0 of the key switches 21and 27' are in contact with their respective break contacts b, and thecapacitor C is charged through the contacts b and c of the switch 21 andthe resistor R, by the power source +B. In this case, if thenon-conductive and no tone signal output appears at the terminal 17.

Under this condition, when the contacts c of the switches 21 and 27 areseparated from their respective break contacts b at an instant t by akeying operation, the capacitor C begins to discharge through theresistor R As a result, a voltage V across the capacitor C decreasesfrom about 12V with the elapse of time and with a time constant T, whichis determined by the values of the capacitor C and resistor R as isindicated in FIG. 4. I

Then, under such conditions of the circuit as a decrease in the voltageof the capacitor C if the contact c of the switch 21 is brought intocontact with the make contact m thereof by a quick keying operation atthe instant t a relatively high voltage V remaining in the capacitor Cwill be applied to the base of the transistor 23 through the contacts 0and m of the switch 21, but if the contact (3 of the switch 21 isbrought into contact with the contact m thereof at another instant I,later than the instant t by a slow keying operation, a voltage.

V lower than the voltage V will be applied to the transitor 23.

Moreover, if the contact 0 of the switch 21 is brought into contact withthe contact in thereof at another instant I, much later than instant tby a very slow keying operation, the capacitor C would have long beenbeing discharged during the time period taken by the considerably slowkeying operation. However, since a divided voltage which is determinedby the resistor R and R is applied across the capacitor C the voltage ofthe capacitor C will be discharged toward that voltage, and consequentlythe resultant voltage of the capacitor C will never be lower than thatdivided voltage.

This will be apparent from the following consideration. As is shown inFIG. 6, the charge-discharge circuit 22 has a D.C. power source V,., thevoltage of which is equal to Vc [R /(R -l-R X 12V, that is, a

voltage across the resistor R The DC power source V,

is connected in series to an equivalent resistance r which is composedof a parallel combination of the resistors R and R thereby forming aseries circuit of r and V This series circuit is equivalent to anarrangement of parallel connection with the capacitor C Accordingly, ifthe instant t, is very much later, the capacitor C is discharged untilthe voltage thereacross becomes equal to the voltage V,, whereupon thecapacitor C ceases and maintains the voltage V,.

Thus, when the voltage V V,,, or V is applied to the transistor 23, thetransistor 23 becomes on or conductive at the instant t t;,, or t.,,respectively to the extent represented by the voltage V,, V or V,-. As aresult, the capacitor C is charged, through the transistor 23, thus madeconductive, to a voltage which is lower.

than the voltage V V; or V by a base-emitter drop voltage V and thevoltage of the capacitor C thus obtained is applied, as an output W ofthe touch responsive keying circuit 11, to the keyer circuit 12. In thisconnection, because the voltage V is substantially maintained by thecapacitor C the output W of a peak value which corresponds to thevoltage V, is obtained for even a long time period after the instant tAs long as the key is depressed and the movable contact 0 of the switch27 is kept in contact with the make contact m, the output W is keptsubstantially constant, discharging very slightly through the transistor23 only.

output W is thus produced by thecircuit 11, the

contacts c of the switches 21 and 27 are returned into A contact withthe contacts b thereof, respectively, by releasing the key, applicationof the charged voltage of 5 the capacitor C to the transistor 23 stops.At the same time the capacitor C is charged through the resistors R andR, by the power source +B, while the capacitor C is discharged throughthe resistors R and R and the switch 27. As a result, the output W ofthe circuit 11 is no longer produced, and the circuit 11 is restored toits original state in which no key is depressed. Consequently, the tonesignal is not emitted from the terminal 17.

Thus, one cycle of the operation of the circuit 11 caused by depressinga key is accomplished; In this one cycle of operation, waveforms of theoutputs W of the circuit are as shown in FIG. 5. The waveforms W W and Wrise with a time constant determined mainly by the capacitance of thecapacitor C and the resistance value of the resistor R at instants 2 tand t respectively, and, furthermore, undergo decay at an instant t,,with a time constant determined mainly by the capacitance of thecapacitor C and the resistances of the resistors R and R The peak valuesof these waveforms correspond to the time periods required for switchingthe key switches 21 and 27, that is, the speeds of the key-depressingoperations.

Another example of the present invention as illustrated in FIG. .7 has atouch-responsive keying circuit 11 further comprising a change-overswitch 25 provided with switching contactsj and k. The contactj isconnected to the contact b ofa key switch 21, while the contact k isconnected to the contact c of the key switch 21 through a resistor 26and a diode 27 as required. Furthermore, a movable contact I isconnected to a power source +8. The diode 27 serves to block a reversecurrent in the case when a plurality of touchresponsive keying circuitsare switched over by using one common change-over switch 25. The othercomponents and their-arrangements are the same as those described withreference to FIG. 3.

In the circuit described above, a touch-responsive output of the circuit11 can be obtained by connecting the movable contact I to the contact j.The other general operations of the circuit are the same as thosedescribed with reference to FIG. 3.

When a touch-irresponsive output is to be produced from the circuit 11,the movable contact I is moved into contact with the contact k. Underthis condition, when the contacts 0 of the switches 21 and 27 arebrought into contact with their respective contacts m by a keyingoperation, i.e., by a depressing the key, predetermined voltage isapplied to the base of the transistor 23 by the power source +B throughthe movable contact 1, the contact k, the resistor 26, the diode 27 andthe contacts c and m of the switch 21.

As a result, the capacitor C is charged to a voltage corresponding tothe predetermined voltage, and the voltage of the capacitor C thusobtained becomes a touch-irresponsive output W of the circuit. In thisconnection, the predetermined voltage is determined by the resistors 26,R and R diode 27, and power source +B.

Thus, the keyer circuit l2 produces a musical tone signal having anenvelope of a certain level keyed by the constant output W. Thisoperation of the circuit 12 is the same as the ordinary operation of aconventional tone keyer circuit, having no touch-responsive circuit, ofan electronic musical instrument.

As is described above, according to the present invention, both thetouch-responsive output which causes the keyer circuit to produce amusical tone sig nal having an envelope of a level determined by thekeying speed and the touchirresponsive output which causes thekeyercircuit to produce a musical tone signal having an envelope of apredetermined level regardless of the keying speed can be selectivelyobtained immediately by merely changing-over the switch 25 withouttroublesome operations.

In addition, even in the case when the keying operation is conductedquickly or slowly as desired in order to obtain the touch-responsiveoutput, the touchresponsive output can be obtained. For this purpose,since the rising time and decay time of the touchresponsive output arecaused to be of a small value of the order of 50ms, the values of thecapacitors of the charge-discharge circuits can be made considerablysmall.

Furthermore, while an example wherein the movable contact I of thechange-over switch 25 is connected to v a common and fixed power source+B has been described above, it is also possible to connect the movablecontact I to a voltage adjustable power source proj vided separatelysuch as shown by dotted lines in FIG. 7 and then to selectively set thelevel of the touchresponsive output W or the level of thetouchirresponsive output W by adjusting the voltage of the adjustablepower source.

Only one touch-responsive. keying circuit 11 is shown in theaccompanying drawings, but in practice a plurality of touch-responsivekeying circuits are provided. In

this case, one changeover switch 25 may be provided in common for thoseplurality of touch-responsive keying circuits, so that the contactsj andk of the switch 25 are connected to the contact b of the switch 21 andthe resistor 26 in each touch-responsive keying circuit.

1 claim: 1. A touch-responsive keying circuit comprising: a

circuit ground; a power source; a key switch having a break contactconnected to said power source, a make contact and a movable contact; afirst charge-discharge circuit having a charging capacitor and adischarging resistor both connected between said movable contact andsaid ground; a transistor having a base connected to said make contact,a collector connected to said power source, and an emitter; and a secondchargedischarge circuit including a second capacitor connected betweensaid emitter and said ground, a second resistor and a second switchconnected in series between said emitter and said ground, said secondswitch being of a normally closed type and gang-operated with said keyswitch.

2. A touch-responsive keying circuit as claimed in claim 1, in whichsaid first charge-discharge circuit is provided with means for applyingacross said charging capacitor a divided voltage of said power source,whereby when the first charge-discharge circuit is discharged, theresultant voltage of the first charge and discharge circuit ismaintained not lower than said divided voltage.

3. A touch-responsive keying circuit as claimed in claim 1 which furthercomprises a change-over switch having a first stationary contactconnected to said power source.

5. A touch-responsive keying circuitas claimed in claim 3, in which aplurality of touch-responsive keying circuits are provided, and onecommon change-over switch is provided for these touch-responsive keyingcircuits.

1. A touch-responsive keying circuit comprising: a circuit ground; apower source; a key switch having a break contact connected to saidpower source, a make contact and a movable contact; a firstcharge-discharge circuit having a charging capacitor and a dischargingresistor both connected between said movable contact and said ground; atransistor having a base connected to said make contact, a collectorconnected to said power source, and an emitter; and a secondcharge-discharge circuit including a second capacitor connected betweensaid emitter and said ground, a second resistor and a second switchconnected in series between said emitter and said ground, said secondswitch being of a normally closed type and gang-operated with said keyswitch.
 2. A touch-responsive keying circuit as claimed in claim 1, inwhich said first charge-discharge circuit is provided with means forapplying across said charging capacitor a divided voltage of said powersource, whereby when the first charge-discharge circuit is discharged,the resultant voltage of the first charge and discharge circuit ismaintained not lower than said divided voltage.
 3. A touch-responsivekeying circuit as claimed in claim 1 which further comprises achange-over switch having a first stationary contact connected to saidcharge-discharge circuit, a second stationary switching contactconnected to the break contact of said key switch, and a movable contactconnected to said power source.
 4. A touch-responsive keying circuit asclaimed in claim 3 in which a movable contact of said change-over switchis connected to a separately provided adjustable power source.
 5. Atouch-responsive keying circuit as claimed in claim 3, in which aplurality of touch-responsive keying circuits are provided, and onecommon change-over switch is provided for these touch-responsive keyingcircuits.